1. Field of the Invention
The invention relates to a multi-beamlet multi-column particle-optical system, in particular a multi-beamlet multi-column particle-optical system comprising a plurality of multi-beamlet particle-optical columns wherein at least one of the multi-beamlet particle-optical columns comprises an electrode element having an aperture of a noncircular shape. The invention further relates to a method of exposing a substrate by multi-beam multi-column exposure using the multi-beamlet multi-column particle-optical system.
2. Brief Description of Related Art
The increasing demand for ever smaller and more complex microstructured devices and the continuing demand for an increase of a throughput in the manufacturing and inspection processes thereof have been an incentive for the development of particle-optical systems that use multiple charged particle beamlets in place of a single charged particle beam, thus significantly improving the throughput of such systems. The use of multiple beamlets is associated with a whole range of new challenges to the design of particle-optical components, arrangements and systems, such as microscopes and lithography systems.
A particle-optical arrangement for forming a plurality of charged-particle beamlets wherein the beamlets are arranged in an array pattern is described in U.S. Pat. Nos. 5,369,282 and 5,399,872, for instance.
Multi-beamlet particle-optical systems make use of a pattern of multiple charged particle beamlets focused on a substrate to be exposed. For example, in an inspection system, a single beam of charged particles is provided by a particle source or, alternatively, multiple beamlets may be provided by an array of charged particle sources. The beam or beamlets is/are then typically directed onto a multi-aperture plate having a plurality of apertures formed therein for generating multiple beamlets from those charged particles of the single beam or beamlets that pass through the apertures of the multi-aperture plate. The multiple beamlets are generally subsequently focused on the substrate, typically by means of a focussing particle-optical lens downstream of the multi-aperture plate. An array of charged particle spots is thus formed on the substrate. Secondary charged particles such as secondary electrons may be emitted by the substrate to be inspected, follow a secondary beamlet path and are incident on a detector.
Further more, in particle-optical lithography, methods of so-called maskless lithography have been established, which, for instance, make use of a blanking aperture array. Such a blanking aperture array typically comprises a multi-aperture plate wherein each of a plurality of apertures is further equipped with a deflecting arrangement, generally comprising electrodes, which, in, a “switched-on” or activated state, is capable of deflecting a beamlet passing through the respective aperture such that it is deflected from a beam path of the beamlets to such an extent that it does not reach the specimen and does not contribute to an exposure of the substrate or specimen. The deflecting arrangements of the individual apertures can thus be switched off or de-activated to let a beamlet pass undisturbed through the respective aperture and a switched-on state where a passing beamlet is deflected away from a beam path and incident on an obstacle in the form of a non-transmitting portion of an aperture or the like such that it will not be incident onto the specimen. By suitable movement of the blanking aperture array relative to the specimen to be exposed and suitable switching sequences of the individual apertures, a pattern can be generated and written onto the specimen, such as described, for instance in US 2003/0155534 A1, the entire content of which is incorporated by reference herein.
In addition to using a plurality of beamlets, systems employing a plurality of two or more particle-optical systems, or columns, operating in parallel to simultaneously expose or inspect the same substrate are being developed. Given that, due to interactions of charged particles, a throughput and a performance of an individual particle-optical system (column) is generally limited by a maximum acceptable current of charged particles in the system, the multi-column approach allows to increase the throughput of such a particle-optical lithography system without further increasing the current through an individual column and therefore avoids a decrease in performance due to space charge effects. Thus, multi-column particle-optical systems comprise a plurality of particle-optical columns which each, in terms of their components and their arrangement, largely correspond to a conventional particle-optical system as described above. An example of a multi-column particle-optical system is described in US Patent Application with publication number US 2005/0104013 A1, the entire content of which is incorporated by reference herein.
Using an array or pattern of beamlets of charged particles requires a multi-beamlet particle-optical system to provide those beamlets in a reliable and accurate manner such that the individual beamlets show little, if any, variation in intensity, deviation from a predetermined position within the array and target position on a substrate, variation in optical properties, such as aberrations and the like. The quality of the pattern of beamlets and, correspondingly, the quality of the pattern of charged particle spots generated in an image or substrate plane, respectively, will generally depend, amongst others, on properties of the beamlet generating arrangement used as well characteristics of the focussing arrangement, such as a lens.
In addition, external factors originating in an environment of the particle-optical system may also influence a performance of the particle-optical system. An example of such an external factor exerting a negative influence on an imaging performance are electromagnetic fields from outside the charged particle system penetrating into the system, as discussed, for instance in US 2005/0072933 A1, the entire content of which is incorporated by reference herein. The electrostatic lens system described therein comprises an electrostatic lens arrangement having more than three electrode elements which are arranged coaxially in series along an optical axis of the electrostatic lens arrangement. Additional shielding is provided by provision of an outer member ring to fill a space between two adjacent electrode elements thus preventing intrusion of interfering electromagnetic fields. The system described therein is a single column system.
In multi-column systems, additional problems arise from the close arrangements of individual columns and their electrostatic and/or electromagnetic fields, which may cause interferences in neighbouring columns. These interferences, for instance a disturbance of a focussing electrostatic and/or electromagnetic field, may cause imaging errors such as particle-optical aberrations and thus deteriorate an imaging performance.
It is therefore an object of the present invention to provide a multi-beamlet multi-column particle-optical system providing an improved imaging performance.
It is a further object of the present invention to provide a multi-beamlet multi-column particle-optical system configured to decrease an influence from one or more neighbouring columns on an imaging performance.
It is another object to provide an improved method of multi-beam multi-column particle-optical exposure.